The present invention relates to an axial piston compressor, especially a compressor for motor vehicle air-conditioning systems, in accordance with the preamble of claim 1.
In the field of compressor drive mechanisms, a trend is beginning to emerge that, in the case of compressors having variable piston stroke, increasing use is being made of tilt plates in the form of a tilt ring, that is to say ring-shaped tilt plates, with a tilt-providing articulation necessary for tilting of the plate being substantially integrated into the ring-shaped tilt plate. For example, there is known, from EP 0 964 997 B1, a compressor in which the stroke movement of the pistons is accomplished by means of engagement—in an engagement chamber—of a ring plate oriented on a slant to the machine shaft. The engagement chamber is provided adjacent to the enclosed hollow space of the piston. For sliding engagement that is substantially free from play in any slanting position of the tilt plate or tilt ring there are provided on both sides, between it and the spherically curved inner wall of the engagement chamber, spherical segments, so-called sliding blocks, so that the tilt ring slides between them as it revolves.
The drive is transmitted from the drive shaft to the tilt ring by a pin for conjoint movement which is attached to the drive shaft and the spherical head of which engages in a radial bore in the tilt ring, the position of the head of the member for conjoint movement being selected so that its center-point coincides with that of the spherical segments. In addition, that center-point is located on a circular line which connects the geometric axes of the seven pistons with one another and, moreover, on a circular line which connects the center-points of the spherical articulation members of the pistons. By that means, the upper dead-center position of the pistons is determined and a minimum clearance volume is ensured. The head shape of the free end of the member for conjoint movement makes it possible for the inclination of the tilt plate to change due to the fact that the head of the member for conjoint movement forms a bearing body for a tilting movement of the tilt plate which changes the stroke distance of the pistons.
A further precondition for tilting of the tilt plate is the displaceability of its mounting axis in the direction of the drive shaft. For this purpose, the mounting axis is formed by two mounting pins mounted on the same axis on each side of a sliding sleeve, which mounting pins are additionally mounted in radial bores in the tilt plate. For this purpose, the sliding sleeve preferably has mounting sleeves on each side, which span the annular space between the sliding sleeve and the tilt plate in the manner of spokes.
The limitation on the displaceability of the mounting axis and, as a result, the maximum angled position of the tilt plate results from the pin for conjoint movement, by virtue of the fact that the latter passes through an elongate hole provided in the sliding sleeve so that the sliding sleeve meets end stops at the ends of the elongate hole. The force for the change in the angle of the tilt plate and, therefore, for regulation of the compressor results from the sum of the pressures acting against one another in each case on each side of the pistons, so that this force is dependent on the pressure in the drive mechanism chamber. In accordance with the prior art, the pressure in the drive mechanism chamber can be regulated between a high pressure and a low pressure and consequently affects the balance of forces at the tilt plate, which influences the inclination of the latter. The position of the sliding sleeve can moreover be influenced by springs which, in various variants, are likewise included in the prior art.
Furthermore, the position of the sliding sleeve, which position governs the delivery output, is also determined by the forces of inertia acting on the tilt plate; the position of the tilt plate, that is to say its angle of tilt or slant, changes with increasing speed of rotation. In the case of modern compressors, the trend is towards using tilt plates having moments of inertia such that they bring about a reduction in the stroke distance of the pistons and therefore a reduction in delivery output when the speed of rotation increases.
However, what is problematic in the arrangement explained hereinbefore is the high Hertzian stress in the region of the head of the member for conjoint movement and the tilt plate (system: sphere/cylinder) and the take-up of the (axial) reaction forces due to the gas force on the pistons and the forces due to the torque to be transmitted to the tilt plate.
A compressor similar to the compressor known from EP 0 964 997 B1 is known from JP 2003-269330 AA, although in that compressor a total of two members for conjoint movement are used.
It is important to the kinematics according to the two mentioned publications, that is to say to the kinematics in the case of the subject-matter of EP 0 964 997 B1 and JP 2003-269330 AA, that the head of the member for conjoint movement centrally coincides with the center-point of the sliding blocks of the pistons and that the position of the center-point of the head of the member for conjoint movement is at the same time approximately tangential to the reference circle of the central axes of the pistons.
Added to the afore-mentioned disadvantageous characteristics is the fact that the subject-matter of EP 0 964 997 B1 and of JP 2003-269330 AA has a very complicated structural arrangement, which results in a high number of parts and therefore high cost, and in addition the mounting by means of two members for conjoint movement is over-determined and therefore susceptible to wear, and the strength of the components, especially due to the fact that a hole is introduced into the shaft, has to be regarded as rather low.
A further compressor is known from DE 101 52 097 A1, differing considerably from the subject-matter of the publications discussed hereinbefore. In the case of the subject-matter according to DE 101 52 097 A1, the member for conjoint movement, in particular the spherical head of the member for conjoint movement, is replaced by a hinge pin or spindle. This is, however, integrated into the tilt plate from the outside and fastened using a cup-shaped disc for conjoint movement which is a component of the drive shaft assembly. The subject-matter of DE 101 52 097 A1 also has a complicated structural arrangement; in addition it has to be borne in mind that a large imbalance can come about, depending on the angle of tilt. This promotes wear on the compressor and as a result reduces its service life.
A further compressor is known from FR 278 21 26 A1, which has a member for conjoint movement extending out from the drive shaft radially and engaging in the tilt plate. In similar manner to the solution according to DE 101 52 097 A1, the tilt plate in this arrangement is also fixed to the member for conjoint movement in radial extension. In this there also lies a central difference from the subject-matter of EP 0 964 997 B1 and JP 2003-269330 AA. Whereas in the latter cases the mounting point of the head of the member for conjoint movement in the tilt plate undergoes relative movement in the guideway (bore) in the tilt plate because the tilt plate performs the rotary movement in an articulation lying on the shaft axis, the rotary movement in the case of the arrangements according to FR 278 21 26 A1 and DE 101 52 097 A1 is accomplished in the lateral articulation of the tilt plate.
In the unpublished Patent Application DE 102 00 404 1645 belonging to the present Applicant, there is proposed a member for conjoint movement which is displaceably mounted in the shaft. As a result, the transmission of force between the head of the member for conjoint movement and the tilt plate can be accomplished optimally (force transmission as a result of area-wise contact). However, the displacement of the member for conjoint movement in the shaft can be problematic because high forces have to be taken up there due to the bending moment and the parts therefore have to be of very rigid construction. This rigid construction causes the compressor to have an increased mass.
From DE 103 154 77 A1 there is known a compressor of the tilt plate/member for conjoint movement construction type wherein the member for conjoint movement does not transmit any torque. This feature in addition also applies to preferred arrangements of DE 102 00 404 1645. The conjoint movement function is restricted to providing support for the piston forces acting axially on the tilt plate, the torque being delivered by further force transmission elements independent of the member for conjoint movement. As a result, the forces acting on the member for conjoint movement are lower because, as already mentioned, no torque is transmitted. The advantage of this approach lies in the fact that the forces or surface contact pressure due to the forces applied (because of the fact that these forces are relatively low) do not cause any excessive deformation at and in the member for conjoint movement, as a result of which the member for conjoint movement can be of correspondingly lightweight construction and tilting of the tilt plate can be accomplished in a relatively hysteresis-free manner. However, a disadvantageous effect can be that the spherical head of the member for conjoint movement is located in a relatively large recess in the tilt plate. As a result, the Hertzian stress can or must be described by a plane/sphere geometric pairing, which is relatively disadvantageous because it causes a high degree of Hertzian stress.
Finally, from the likewise unpublished DE 10 2005 004 840 belonging to the present Applicant, there is known a compressor which provides an improvement in respect of the problem of surface contact pressure. The subject-matter of DE 10 2005 004 840 includes a support element in engagement with a tilt ring, with line contact arising between the support element and the tilt ring. Compared to the previously described prior art, this constitutes an improvement in respect of the Hertzian stress. A likewise advantageous effect is that, in the case of the subject-matter of DE 10 2005 004 840, a drive moment and a torsional moment are decoupled from the gas force support. However, a relatively large recess is necessary in the tilt plate in order to ensure thereby a sufficient length of line contact and to achieve correspondingly low surface contact pressure. The large recess in the tilt plate could, because of the gas forces to be transferred, result in deformation of the tilt ring and therefore in wear. Furthermore, the down-regulating behaviour of the tilt plate (which is dependent on the moment of deviation relative to the tilt-providing articulation) and also the imbalance thereof are disadvantageously affected by a large recess. In the case of the subject-matter of DE 10 2005 004 840 the mass of the gas force support does not affect the moment of deviation.